Previous work established that the flow cytometric dihydrorhodamine (DHR)-based assay for evaluation of oxidative burst is a sensitive method for evaluating phagocytes in patients with possible chronic granulomatous disease (CGD). It has also been useful as an accurate test for screening possible X-linked CGD carriers and a preliminary screen for the genotype of the disease. The method was optimized and is sensitive to one normal cell in less than or equal to 10,000 abnormal cells. A project was undertaken to track granulocytes post-transfusion in CGD patients following allogeneic leukocyte transfusions and this assay has proven to be very reliable in establishing duration of transfused cell survival and allsensitization. The results of this study were presented at the American Association of Blood Banks annual meeting. The second phase of gene therapy of CGD continues directed at patients with X-linked CGD. The DHR assay is being applied as a critical method for establishing the presence of gene-corrected granulocytes in the circulation and monitoring the duration of production of the gene-corrected cells in the treated patients